U.S. patent application number 12/448410 was filed with the patent office on 2010-06-10 for level monitoring device for determining and monitoring a fill level of a medium in the process area of a vessel.
This patent application is currently assigned to ENDRESS + HAUSER GMBH + CO.KG. Invention is credited to Eric Bergmann, Klaus Feisst.
Application Number | 20100141505 12/448410 |
Document ID | / |
Family ID | 39431840 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100141505 |
Kind Code |
A1 |
Bergmann; Eric ; et
al. |
June 10, 2010 |
LEVEL MONITORING DEVICE FOR DETERMINING AND MONITORING A FILL LEVEL
OF A MEDIUM IN THE PROCESS AREA OF A VESSEL
Abstract
A fill level measuring device for ascertaining and monitoring
fill level of a medium in the process space of a container by means
of a microwave travel time measuring method. The device includes:
measurement transmitter; and an antenna unit, which is constructed
at least of a hollow conductor and a radiating element, wherein a
process isolation element is inserted into the hollow conductor for
process isolation between measurement transmitter and the process
contacting, radiating element. The process isolation element is
made of a ceramic material and includes at least one glass layer,
via which the process isolation element is directly glass bonded in
the hollow conductor in a glass bonding region.
Inventors: |
Bergmann; Eric; (Steinen,
DE) ; Feisst; Klaus; (Kirchzarten, DE) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE, FOURTH FLOOR
ALEXANDRIA
VA
22314-1176
US
|
Assignee: |
ENDRESS + HAUSER GMBH +
CO.KG
Masulburg
DE
|
Family ID: |
39431840 |
Appl. No.: |
12/448410 |
Filed: |
December 6, 2007 |
PCT Filed: |
December 6, 2007 |
PCT NO: |
PCT/EP2007/063464 |
371 Date: |
November 12, 2009 |
Current U.S.
Class: |
342/124 |
Current CPC
Class: |
G01S 13/88 20130101;
H01Q 1/225 20130101; G01F 23/284 20130101; H01P 1/08 20130101; H01Q
13/02 20130101; G01S 7/03 20130101 |
Class at
Publication: |
342/124 |
International
Class: |
G01F 23/284 20060101
G01F023/284 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2006 |
DE |
10 2006 062 223.5 |
Claims
1-14. (canceled)
15. A fill-level measuring device for ascertaining and monitoring
fill level of a medium located in a process space of a container by
means of a method measuring travel time of microwaves, said device
comprising: a measurement transmitter; an antenna unit, which is
constructed at least of a hollow conductor and a radiating element;
and a process isolating element transmissive for microwaves is
inserted in said hollow conductor, between said measurement
transmitter and said radiating element contacting the process, for
process isolation, wherein: said process isolating element
comprises a ceramic material and at least one glass layer, via
which said process isolating element is bonded in a glass bonding
region directly to said hollow conductor.
16. The apparatus as claimed in claim 15, further comprising: at
least one graphite packing ring on the process side, which has an
additional sealing action and protects said at least one glass
layer of the direct glass bonding on the process-side against
corrosion from the medium.
17. The apparatus as claimed in claim 15, wherein: at least one
partially applied, corrosion resistant coating is provided on the
process-side on said glass layer, which protects said glass layer
of the direct glass bonding on the process-side against corrosion
from the medium.
18. The apparatus as claimed in claim 16, wherein: said hollow
conductor is constructed of a plurality of parts, including at
least a first element and a second element.
19. The apparatus as claimed in claim 18, wherein: securement by
means of a screwed connection of said first element and said second
element is provided, which effects an additional sealing action due
to compression exerted on said graphite packing ring.
20. The apparatus as claimed in claim 15, wherein: a surrounding
weld seam is provided on the outer surface of said hollow
conductor, which secures a location of separation of said first
element and said second element of said hollow conductor against
rotation.
21. The apparatus as claimed in claim 15, wherein: said at least
one glass layer has a thickness of 0.5 to 5 millimeters.
22. The apparatus as claimed in claim 15, wherein: on the
process-side, a microwave transmissive, corrosion resistant coating
is provided on said glass-bonded, process isolating element and/or
the inner surface of said hollow conductor.
23. The apparatus as claimed in claim 15, wherein: said ceramic,
process isolating element is embodied as an matching cone, whose
cross section in a matching region conically tapers starting from a
glass bonding region of the zonal, direct glass bonding of the
matching cone in said hollow conductor, in at least one step and at
at least one angle.
24. The apparatus as claimed in claim 15, wherein: a hermetically
sealed, hollow space is provided in the interior of said ceramic,
process isolating element.
25. The apparatus as claimed in claim 24, wherein: a microwave
transmissive fill material with a smaller permittivity is provided
in the hermetically sealed, hollow space of said ceramic, process
isolating element.
26. The apparatus as claimed in claim 15, wherein: a single step or
multistep, linearly decreasing inner diameter of said hollow
conductor is provided in a matching region of said process
isolating element in the direction of the zonal, direct glass
bonding.
27. The apparatus as claimed in claim 15, wherein: provided as
material for said hollow conductor is a stainless steel tube or a
ceramic, or plastic, tube coated with metal on inner surfaces.
28. The apparatus as claimed in claim 15, wherein: a planar
antenna, a parabolic antenna, a horn antenna or a rod antenna is
provided as said antenna unit.
Description
[0001] The present invention relates to a fill level measuring
device for ascertaining and monitoring fill level of a medium in
the process space of a container, as such device is defined in the
preamble of claim 1.
[0002] One measuring method, out of a number of measuring methods
for ascertaining fill level in a container, is the travel time
measuring method. With this measuring method, for example,
microwaves are radiated via an antenna device and the waves
reflected on the surface of the medium are detected, with the
travel time of the measuring signal being a measure of distance.
From half the travel time, the fill level of the medium in a
container can, in this way, be ascertained. The echo curve
represents, here, the entire curve of the signal as a function of
time, with each measured value of the echo curve corresponding to
an amplitude of an echo signal reflected at a surface at a certain
distance. The travel time measuring method is essentially divided
into two evaluation methods: In the time difference measurement
method, the time, which a broadband wave, signal pulse requires for
a traveled distance, is determined. In the frequency modulated,
continuous wave method (FMCW--Frequency Modulated Continuous Wave),
the transmitted, frequency-modulated, high frequency signal is
compared with the reflected, received, frequency-modulated, high
frequency signal. In the following, no restriction is made to any
particular method of measurement.
[0003] In the case of certain process applications, fill level
measuring devices are exposed to extreme conditions, for example
high temperatures, high pressures and/or chemically aggressive
substances. In particular, microwave, fill level measuring devices
contain temperature, and/or pressure, sensitive components. These
include, for example, measuring device electronics and transmission
and/or reception elements for the microwaves.
[0004] Insertion of a hermetically sealed, process isolation
element into the hollow conductor of the antenna ensures highest
possible safety, since a second "safety element" seals the process,
during an isolating of the modular, measurement active parts, such
as e.g. a coupling element/exciter element or the measuring device
electronics, from the measurement passive parts, such as e.g. the
antenna, for maintenance or repair.
[0005] This problematic and a solution therefor are considered in
EP 0 943 902 A1. There, a fill level measuring device working with
microwaves is described for high temperature applications. The
device has an antenna and includes a process isolation element in
the hollow conductor region of the antenna. A glass window, among
others, is described as a process isolation element. These glass
windows protect the sensitive components of the fill level
measuring devices against extreme measurement conditions, such as
high temperatures, high pressures, and chemically aggressive media.
A disadvantage of this design of the process isolation element is
that the glass window must, because of the available production
technology, for example due to the different material expansions,
be provided in a thin-walled metal sleeve. This sleeve with the
glass window must be soldered or welded in further, complicated,
working steps into the hollow conductor. This requires a high
additional work effort associated with the production of the
antenna of the fill level measuring device. In addition, with the
many working steps, manufacturing costs and safety risk are
increased due to manufacturing errors.
[0006] US 2005/0253751 A1 describes a modular construction of a
horn antenna. The process isolation element is constructed in the
form of a ceramic, matching cone that is introduced into the hollow
conductor and sealed by graphite packing rings. This design has the
disadvantage that a sealing against gas diffusion and a temperature
resistant, process isolation are not achieved.
[0007] In DE 199 50 429 A1, a ceramic process isolation element is
described that is shrunk fit into the hollow conductor.
Disadvantageous, here, is that, despite polished bounding surfaces
on the process isolation element and in the waveguide, no seal is
achieved. Further, the large compressive forces that act on the
ceramic, process isolation element can lead to stress cracks.
[0008] A disadvantage of the aforementioned examples of embodiments
of a state of the art process isolation element is that manufacture
is very complex and expensive. In order to obtain a connection
impervious to gas diffusion between a ceramic and a surrounding
metal, hollow conductor, only a soldering procedure is well-known
according to the state of the art. In such case, the ceramic, as
process isolation element, is first metallized on the surface in
complex working steps, then soldered into a soldering sleeve, which
has a coefficient of thermal expansion similar to that of the
ceramic (e.g. Kovar), and this finally is welded into a stainless
steel, hollow conductor. Other joining techniques, such as, for
example, shrink fitting at high temperature, always have a certain
leakage rate and are not impervious to gas diffusion, as already
mentioned.
[0009] An object of the invention is to provide a fill level
measuring device having a gas diffusion resistant, process
isolation element for process isolation, which does not exhibit the
disadvantages specified above, and which, in particular, can be
produced economically and simply.
[0010] This object of the invention is achieved by the features set
forth in claim 1.
[0011] Advantageous further developments of the invention are
specified in the dependent claims.
[0012] Further details, characteristics, and advantages of the
subject matter of the invention will be understood from the
following description in combination with the associated drawings,
in which advantageous embodiments of the invention are presented.
In the embodiments of the invention presented in the figures of the
drawing, in order not to clutter and for simplification, components
or groups of components, which correspond in their structure and/or
in their function, are given equal reference characters. The
figures of the drawing show as follows:
[0013] FIG. 1 a schematic representation of an antenna unit
equipped, fill level measuring device of process measurements
technology, and
[0014] FIG. 2 longitudinal, sectional view of the hollow conductor
of the antenna unit of FIG. 1, having a process isolation element
according to the invention.
[0015] FIG. 1 shows a fill level measuring device 1 of process
measurements technology used for determining fill level 2 in a
container 4. The fill level measuring device is composed,
fundamentally, of an antenna unit 7 and a measurement transmitter
23. The antenna unit 7 includes in the hollow conductor 8, in this
example of an embodiment, a process isolation element 11 of the
invention. The fill level measuring device 1, which is mounted via
a process connection 35 onto a container 4, ascertains, for example
by the travel time measurement method, the level 2 of a medium 3
and/or fill substance in the container 4. The antenna unit 7 is, in
this example of an embodiment, provided in the form of a horn
antenna. The process isolation element 11 of the invention is also
deployable with other types of antenna units, such as, for example,
rod antennas, planar antennas, parabolic antennas, and in measuring
systems of time domain reflectometry working with a waveguide-led
microwave. The antenna unit 7 can be divided into two fundamental,
functional units--the hollow conductor 8 and the radiating element
12.
[0016] Provided in the measurement transmitter 23 is a
transmitting/receiving unit 27, in which the microwave measuring
signals 6 are produced. Via a coupling element 33, the microwave
measuring signals 6 are coupled into the hollow conductor 8 of the
antenna unit 7. The coupling element 33 is installed in the hollow
conductor 8 via a gas diffusion blocking, glass feedthrough. The
microwave measurement signals 6 coupled into the hollow conductor 8
of the antenna unit 7 are radiated, in given cases, through a
filling element 36, from the radiation element 10, as sent, or
transmission, signals S into the process space 5 with a
predetermined radiation characteristic. Usually the aim is to have
a radiation characteristic of the microwave measuring signals
exhibiting a planar wave front, in order to avoid travel time
differences in the reflection signals R. The microwave measuring
signals 6 transmitted into the measurement space 5 are reflected on
the surface of the medium 3 and received, after a certain travel
time, back at the transmitting/receiving unit 27. From the travel
time of the microwave measurement signal 6, the fill level 2 of the
medium 3 in the container 4 is determined.
[0017] The control/evaluation unit 26 in the measurement
transmitter 23 has the task of evaluating the received reflection
signals R of the microwave measuring signals 6, using further
processing of the measurement signal 6 by signal processing and
special, signal evaluating algorithms, as an echo curve, and
therefrom, the travel time, or the fill level 2, is
ascertained.
[0018] The control/evaluation unit 26 communicates via a
communication interface 28 with a remote control location and/or
with additional fill-level measuring devices 1, which are not
explicitly shown. Via the supply line 29, the fill-level measuring
device 1 can be supplied with the required energy. This additional
supply line 29 for energy supply of the fill-level measuring device
1 is absent, when the device is a so called two-conductor measuring
device, whose communication and energy supply take place via the
fieldbus 30 exclusively and simultaneously via a two-wire line. The
data transmission, or communication, via the fieldbus 30 occurs,
for example, according to the CAN, HART, PROFIBUS DP, PROFIBUS FMS,
PROFIBUS PA, or FOUNDATION FIELDBUS standard.
[0019] FIG. 2 presents a sectional view of an example of an
embodiment of the hollow conductor 8 with the glass bonded,
ceramic, process isolating element 11 of the invention. According
to the invention, a ceramic matching cone 22 transmissive for
microwaves is provided, which is melt bonded in a metal, hollow
conductor 8 by means of a 1-2 mm thick, annular glass layer 15. The
hollow conductor 8 is, in this case, embodied in the form of a
round, hollow conductor. However, any other form of hollow
conductor 8 can be used for the installation of the invention of
the matching cone 22 by means of glass bonding. Through glass
bonding of the ceramic matching cone 22 in the hollow conductor 8,
there is achieved a gas diffusion blocking, microwave transmissive,
process isolation, which is well suited for use in the face of high
temperatures, high pressures and aggressive process conditions.
Disadvantageous with a glass layer 15 contacting the process,
however, is that glass is corroded by steam. In order to avoid this
corrosion of the thin glass layer 15, a graphite packing ring 16 is
placed in front of the glass layer 15 for protecting it. The
sealing action of the graphite packing ring 16 is achieved by
executing the hollow conductor 8 in two parts and, by a screwed
connecting of the two elements 9,10 of the hollow conductor 8, a
compressive force is exerted on the graphite packing ring 16.
Additionally, a corrosion resistant coating 37 can be applied
partially on the glass layer 15. This corrosion resistant coating
37 can be produced, for example, through vapor deposition of a
chromium/gold coating. A graphite packing ring 16 as corrosion
protection of the glass layer 15 is, due to the corrosion
protection from the application of a corrosion resistant coating
37, then no longer absolutely necessary. However, the graphite
packing ring 16 then provides an additional sealing action.
[0020] Through introduction of the process isolating element 11
into the hollow conductor 8, the wave resistance of the conductor
system is altered. In order to match this wave resistance, the
hollow conductor is tapered, especially in the matching region 14.
The process isolating element 11 includes an matching cone 22
having a cylindrical shape, which tapers in the matching region 14
toward both end faces at a certain angle 24, and which has, thus,
on both sides at least one step or multistep, conical appendages.
The embodiment of the process isolating element 11 as matching cone
22 has, as a result, that the maximum diameter of the cone is
larger than the minimum diameter of the hollow conductor 8 at the
position of maximum necking. For this reason, it can be necessary
to make the hollow conductor 8 in two parts at the location of the
glass bonding, or introduction, and to provide there a location of
separation 20.
[0021] In this example of an embodiment, the hollow conductor 8 is,
such as already mentioned, constructed of two units, a first
element 9 and a second element 10, which are connected with one
another via a screwed connection 19. At the location of separation
21, the first element 9 and the second element 10 are welded
together gas tightly via a radially surrounding, weld seam on the
outer surface 32, or at the location of separation 20. This two
part construction of the hollow conductor 8 is necessary in this
example of an embodiment, since, first of all, the process
isolating element 11 is embodied as matching cone 22 for matching
the wave resistance, and, secondly, because, for protection of the
glass layer against steam, an additional graphite packing ring is
placed in front of it as a supplemental sealing element.
[0022] For lessening the attenuation of the microwaves 6, for
example, a hollow space 18 is provided in the process isolating
element 11 and filled with a dielectric, fill material 38. This
fill material 38 has, relative to the ceramic of the matching cone
22, a much smaller permittivity, or dielectric constant, whereby
the intensity of the microwaves 6 is not strongly attenuated by the
fill material 38. Furthermore, selected as fill material 38 is, for
example, a material having a small thermal expansion, e.g.
ROHACELL, a material comprising hollow glass spheres or additional,
temperature compensated fillers.
[0023] The matching cone 22 is, according to the invention,
inserted in the first element 9 of the hollow conductor 8. In such
case, a glass substrate is introduced either as powder or
prefabricated ring into a free gap in the glass bonding region 13
and melted by a predetermined temperature cycle in a furnace. Used
as glass substrate are, for example, glasses usual for glass
feedthroughs. In the melted state, the glass layer 15 brings about
with the metal, hollow conductor 8 and/or the ceramic matching cone
22 a material bonded interlocking, gas diffusion blocking
connection. Furthermore, another option is to apply a glass layer
15 directly on the ceramic body of the matching cone 22 and to use
this prefabricated part in the seat provided therefor in the first
element 9 of the hollow conductor 8. The application of a thin
glass layer 15 of some millimeters can occur, for example, also
using a chemical or physical gas phase deposit coating method (CVD,
PVD). The heating of the glass layer 15 can, for example, also be
achieved by radiating highly energetic microwaves with a high
intensity focused on the glass layer 15, so that a strong heating
is produced only zonally in the glass bonding region 13. Once the
matching cone 22 is bonded via the glass layer 15 in the first
element 9 of the hollow conductor 8 and, in given cases, a
corrosion resistant coating 37 applied, then the graphite packing
ring 16 is pressed via the screwed connection 19 of the second
element 10 of the hollow conductor 8 fixedly into the cavity
provided below the glass layer 15. Advantageously, the expansion
coefficients of the materials of the matching cone 22, the hollow
conductor 8 and the glass layer 15 are so matched to one another,
that no extreme stresses, or even stress cracks, occur in the
material composite. The matching cone 22 is, for example, made of a
technical-grade, aluminum oxide ceramic.
[0024] For increasing the quality of sealing and the corrosion
resistance, the ceramic matching cone 22 bonded by the glass in the
hollow conductor 8, and the inner surfaces 31 of the hollow
conductor 8 can even be provided with an additional coating 17.
This coating can be produced, for example, by a simple chemical or
physical gas phase deposit, coating method (CVD, PVD).
[0025] A further advantage of the glass bonding in comparison to
soldering is that no complicated surface preparation, such as
polishing, or hardening, or curing, of the ceramic and no expensive
materials, such as e.g. Kovar for the soldering sleeve, are
required. Moreover, the manufacture of the process isolating
element 11 and its glass bonding in the hollow conductor 8 are
clearly easier and therewith significantly more cost effective.
[0026] The process isolating element 11 of the invention delivers
other advantages, for instance, that the coupling element 33 in the
case of condensate formation, and/or the electronics and the
coupling element 33, can be removed, since in a first safety stage,
the measurement-inactive parts of the antenna unit 7, such as, for
example, the flange-plating of the filling element 36 seal the
process to the outside and the process isolating element 11 forms a
second safety stage (second line of defense). In this way, an
option is provided, in the case of an alteration or repair of the
fill-level measuring device 1, to mount the measurement transmitter
23 on the antenna unit 7, with the process being in a sealed state.
Depending on embodiment and application, the fill-level measuring
device 1 can be composed of different modules. An alteration of the
fill-level measuring device 1 to use another type of coupling, e.g.
step, or pin, coupling, or another frequency, e.g. 6 GHz or 26 GHz,
is possible through the isolation of the active parts from the
passive parts with the process being in a sealed state. The
coupling element 33 is, for example, modularly embodied and can be
inserted via a screwed connection into the hollow conductor 8.
LIST OF REFERENCE CHARACTERS
TABLE-US-00001 [0027] TABLE 1 1 fill level measuring device 2 fill
level 3 medium 4 container 5 process space 6 microwaves, microwave
measuring signal 7 antenna unit 8 hollow conductor 9 first element
10 second element 11 process isolating element 12 radiating element
13 glass bonding region 14 matching region 15 glass layer 16
graphite packing ring 17 coating 18 hollow space 19 screwed
connection 20 weld seam 21 separation 22 matching cone 23
measurement transmitter 24 angle 25 stage 26 control unit (open or
closed loop) 27 transmitting/receiving unit 28 communication
interface 29 supply line 30 communication line 31 inner surface 32
outer surface 33 coupling element 34 glass feedthrough 35 process
connection 36 fill body 37 corrosion resistant coating 38 fill
substance R reflection signals S transmission signals
* * * * *